This invention relates to the use of N-formyl hydroxylamine derivatives as antibacterial agent
In general, bacterial pathogens are classified as either Gram-positive or Gram-negative. Many antibacterial agents (including antibiotics) are specific against one or other Gram-class of pathogens. Antibacterial agents effective against both Gram-positive and Gram-negative pathogens are therefore generally regarded as having broad spectrum activity.
Many classes of antibacterial agents are known, including the penidillins and cephalosporins, tetracyclines, sulfonamides, monobactams, fluoroquinolones and quinolones, aminoglycosides, glycopeptides, macrolides, polymyxins, lincosamides, trimethoprim and chloramphenicol. The fundamental mechanisms of action of these antibacterial classes vary.
Bacterial resistance to many known antibacterials is a growing problem. Accordingly there is a continuing need in the art for alternative antibacterial agents, especially those which have mechanisms of action fundamentally different from the known classes.
Amongst the Gram-positive pathogens, such as Staphylococci, Streptococci, Mycobacteria and Enterococci, resistant strains have evolvedlarisen which makes them particularly difficult to eradicate. Examples of such strains are methicillin resistant Staphylococcus aureus (MRSA), methicillin resistant coagulase negative Staphylococci (MRCNS), penicillin resistant Streptococcus pneumoniae and multiply resistant Enterococcus faecium. 
Pathogenic bacteria are often resistant to the aminoglycoside, xcex2-lactam (penicillins and cephalosporins), and chloramphenicol types of antibiotic. This resistance involves the enzymatic inactivation of the antibiotic by hydrolysis or by formation of inactive derivatives. The xcex2-lactam (penicillin and cephalosporin) family of antibiotics are characterised by the presence of a xcex2-lactam ring structure. Resistance to this family of antibiotics in clinical isolates is most commonly due to the production of a xe2x80x9cpenicillinasexe2x80x9d (xcex2-lactamase) enzyme by the resistant bacterium which hydrolyses the xcex2-lactam ring thus eliminating its antibacterial activity.
Recently there has been an emergence of vancomycin-resistant strains of enterococci (Woodford N. 1998 Glycopeptide-resistant enterococci: a decade of experience. Journal of Medical Microbiology. 47(10):849-62). Vancomycin-resistant enterococci are particularly hazardous in that they are frequent causes of hospital based infections and are inherently resistant to most antibiotics. Vancomycin works by binding to the terminal D-Ala-D-Ala residues of the cell wall peptidioglycan precursor. The high-level resistance to vancomycin is known as VanA and is conferred by a genes located on a transposable element which alter the terminal residues to D-Ala-D-lac thus reducing the affinity for vancomycin.
In view of the rapid emergence of multidrug-resistant bacteria, the development of antibacterial agents with novel modes of action that are effective against the growing number of resistant bacteria, particularly the vancomycin resistant enterococci and xcex2-lactam antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus, is of utmost importance.
This invention is based on the finding that certain hydroxamic acid and N-formyl hydroxylamine derivatives have antibacterial activity, and makes available a new class of antibacterial agents. The inventors have found that the compounds with which this invention is concerned are antibacterial with respect to a range of Gram-positive and Gram-negative organisms.
Although it may be of interest to establish the mechanism of action of the compounds with which the invention is concerned, it is their ability to inhibit bacterial growth that makes them useful. However, it is presently believed that their antibacterial activity is due, at least in part, to intracellular inhibition of bacterial polypeptide deformylase (PDF; EC 3.5.1.31).
All ribosome-mediated synthesis of proteins starts with a methionine residue. In prokaryotes the methionyl moiety carried by the initiator tRNA is N-formylated prior to its incorporation into a polypeptide. Consequently, N-formylmethionine is always present at the N-terminus of a nascent bacterial polypeptide. However, most mature proteins do not retain the N-formyl group or the terminal methionine residue. Deformylation is required prior to methionine removal, since methionine aminopeptidase does not recognise peptides with an N-terminal formylmethionine residue (Solbiati et al., J. Mol. Biol. 290:607-614, 1999). Deformylation is, therefore, a crucial step in bacterial protein biosynthesis and the enzyme responsible, PDF, is essential for normal bacterial growth. Although the gene encoding PDF (def) is present in all pathogenic bacteria for which sequences are known (Meinnel et al., J. Mol. Biol, 266:939-49, 1997), it has no eukaryotic counterpart, making it an attractive target for antibacterial chemotherapy.
The isolation and characterisation of PDF has been facilitated by an understanding of the importance of the metal ion in the active site (Groche et al., Biophys. Biochem. Res. Commun., 246:324-6, 1998). The Fe2+ form is highly active in vivo but is unstable when isolated due to oxidative degradation (Rajagopalan et al., J. Biol. Chem. 273:22305-10, 1998). The Ni2+ form of the enzyme has specific activity comparable with the ferrous enzyme but is oxygen-insensitive (Ragusa et al., J. Mol. Biol. 1998, 280:515-23, 1998). The Zn2+ enzyme is also stable but is almost devoid of catalytic activity (Rajagopalan et al., J. Am. Chem. Soc. 119:12418-12419, 1997).
Several X-ray crystal structures and NMR structures of E. coli PDF, with or without bound inhibitors, have been published (Chan et al., Biochemistry 36:13904-9, 1997; Becker et al., Nature Struct. Biol. 5:1053-8, 1998; Becker et al., J. Biol. Chem. 273:11413-6, 1998; Hao et al., Biochemistry, 38:4712-9, 1999; Dardel et al., J. Mol. Biol. 280:501-13, 1998; O""Connell et al., J. Biomol. NMR, 13:311-24, 1999), indicating similarities in active site geometry to metalloproteinases such as thermolysin and the metzincins.
Recently the substrate specificity of PDF has been extensively studied (Ragusa et al., J. Mol. Biol. 289:1445-57, 1999; Hu et al., Biochemistry 38:643-50, 1999; Meinnel et al., Biochemistry, 38:4287-95, 1999). These authors conclude that an unbranched hydrophobic chain is preferred at P1xe2x80x2, while a wide variety of P2xe2x80x2 substituents are acceptable and an aromatic substituent may be advantageous at the P3xe2x80x2 position. There have also been reports that small peptidic compounds containing an H-phosphonate (Hu et al., Bioorg. Med. Chem. Lett., 8:2479-82, 1998) or thiol (Meinnel et al., Biochemistry, 38:4287-95, 1999) metal binding group are micromolar inhibitors of PDF. Peptide aldehydes such as calpeptin (N-Cbz-Leu-norleucinal) have also been shown to inhibit PDF (Durand et al., Arch. Biochem. Biophys., 367:297-302, 1999). However, the identity of the metal binding group and its spacing from the rest of the molecule (xe2x80x9crecognition fragmentxe2x80x9d) has not been studied extensively. Furthermore, non-peptidic PDF inhibitors, which may be desirable from the point of view of bacterial cell wall permeability or oral bioavailability in the host species, have not been identified.
Certain N-formyl hydroxylamine derivatives have previously been claimed in the patent publications listed below, although very few examples of such compounds have been specifically made and described:
The pharmaceutical utility ascribed to the N-formyl hydroxylamine derivatives in those publications is the ability to inhibit matrix metalloproteinases (MMPs) and in some cases release of tumour necrosis factor (TNF), and hence the treatment of diseases or conditions mediated by those enzymes, such as cancer and rheumatoid arthritis. That prior art does not disclose or imply that N-formyl hydroxylamine derivatives have antibacterial activity.
In addition to these, U.S. Pat. No. 4,738,803 (Roques et al.) also discloses N-formyl hydroxylamine derivatives, however, these compounds are disclosed as enkephalinase inhibitors and are proposed for use as antidepressants and hypotensive agents. Also, WO 97/38705 (Bristol-Myers Squibb) discloses certain N-formyl hydroxylamine derivatives as enkephalinase and angiotensin converting enzyme inhibitors. This prior art does not disclose or imply that N-formyl hydroxylamine derivatives have antibacterial activity either.
Our copending Intentional Patent Application No. WO 99/39704 describes and claims, inter alia, the use of a compound of formula (I) or a pharmaceutically or veterinarily acceptable salt thereof in the preparation of an antibacterial composition: 
wherein R1 represents hydrogen, C1-C6 alkyl or C1-C6 alkyl substituted by one or more halogen atoms; R2 represents a substituted or unsubstituted C1xe2x80x94C6 alkyl, cycloalkyl(C1-C6 alkyl)xe2x80x94 or aryl(C1-C6 alkyl)xe2x80x94 group; and A represents a group of formula (IA), or (IB): 
wherein R4 represents the side chain of a natural or non-natural alpha amino acid, and R5 and R6 when taken together with the nitrogen atom to which they are attached form an optionally substituted saturated heterocyclic ring of 3 to 8 atoms which ring is optionally fused to a carbocyclic or second heterocyclic ring.
Very many hydroxamic acid derivatives are known. Many have been disclosed as having matrix metalloproteinase (MMP) inhibitory activity, and thus to be potentially useful for the treatment of diseases mediated by MMPs, for example cancer, arthritides, and conditions involving tissue remodeling such as wound healing, and restenosis. In addition our International Patent Application No. PCT/GB99/01541 describes the use of analogues of the N-formylhydroxylamine derivatives of WO 99/39704 (wherein the N-formylhydroxylamine group is replaced by a hydroxamic acid group) in the preparation of an antibacterial composition.
According to the first aspect of the present invention there is provided the use of a compound of formula (I) or a pharmaceutically or veterinarily acceptable salt, hydrate or solvate thereof in the preparation of an antibacterial composition: 
wherein:
R1, represents hydrogen, C1-C6 alkyl or C1-C6 alkyl substituted by one or more halogen;
R2 represents a group R10xe2x80x94(X)nxe2x80x94(ALK)xe2x80x94 wherein
R10 represents hydrogen, a C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, cycloalkyl, aryl, or heterocyclyl group, any of which may be unsubstituted or substituted by (C1-C6)alkyl, (C1-C6)alkoxy, hydroxy, mercapto, (C1-C6)alkylthio, amino, halo (including fluoro, chloro, bromo and iodo), trifluoromethyl, cyano, nitro, xe2x80x94COOH, xe2x80x94CONH2, xe2x80x94COORA, xe2x80x94NHCORA, xe2x80x94CONHRA, xe2x80x94NHRA, xe2x80x94NRARB, or xe2x80x94CONRARB wherein RA and RB are independently a (C1-C6)alkyl group, and
ALK represents a straight or branched divalent C1-C6 alkylene, C2-C6 alkenylene, C2-C6 alkynylene radical, and may be interrupted by one or more non-adjacent xe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94 linkages,
X represents xe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94 or xe2x80x94Sxe2x80x94, and
n is 0 or 1;
R represents hydrogen or C1-C6 alkyl,
R3 represents the characterising group of a natural or non-natural a amino acid in which any functional groups may be protected; and
R4 represents an ester or thioester group,
or a pharmaceutically acceptable salt, hydrate or solvate thereof.
In another aspect, the invention provides a method for the treatment of bacterial infections in humans and non-human mammals, which comprises administering to a subject suffering such infection an antibacterially effective dose of a compound of formula (I) as defined above.
In a further aspect of the invention there is provided a method for the treatment of bacterial contamination by applying an antibacterially effective amount of a compound of formula (I) as defined above.
In a further aspect of the invention there is provided a pharmaceutical or veterinary composition comprising a compound as defined by reference to formula (I) above, together with a pharmaceutically or veterinarily acceptable excipient or carrier.
Compositions of the invention may additionally include an antibacterial agent other than one defined by reference to formula (I) above.
In addition to their pharmaceutical or veterinary use, the compounds of the invention may also be of use as component(s) of general antibacterial cleaning or disinfecting materials.
According to a preferred embodiment, the various aspects of the invention can be applied against xe2x80x9cxcex2-lactamxe2x80x9d-resistant bacteria and the infections they cause.
As defined herein, xe2x80x9cxcex2-lactamxe2x80x9d-resistant bacteria are those bacteria that are resistant to antibiotics characterised by the presence of a xcex2-lactam ring. Such compounds are more commonly known in the art as members of the penicillin or cephalosporin families of compounds. Methicillin-resistant Staphylococcus aureus is an example of a xe2x80x9cxcex2-lactamxe2x80x9d-resistant bacterium (also referred to herein as xcex2-lactam antibiotic-resistant bacterium).
As used herein the term xe2x80x9c(C1-C6)alkylxe2x80x9d means a straight or branched chain alkyl moiety having from 1 to 6 carbon atoms, including for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl and n-hexyl.
As used herein the term xe2x80x9cdivalent (C1-C6)alkylene radicalxe2x80x9d means a saturated hydrocarbon chain having from 1 to 6 carbon atoms and two unsatisfied valencies.
As used herein the term xe2x80x9c(C2-C6)alkenylxe2x80x9d means a straight or branched chain alkenyl moiety having from 2 to 6 carbon atoms having at least one double bond of either E or Z stereochemistry where applicable. The term includes, for example, vinyl, allyl, 1- and 2-butenyl and 2-methyl-2-propenyl.
As used herein the term xe2x80x9cdivalent (C2-C6)alkenylene radicalxe2x80x9d means a hydrocarbon chain having from 2 to 6 carbon atoms, at least one double bond, and two unsatisfied valencies.
As used herein the term xe2x80x9cC2-C6 alkynylxe2x80x9d refers to straight chain or branched chain hydrocarbon groups having from two to six carbon atoms and having in addition one triple bond. This term would include for example, ethynyl, 1-propynyl, 1- and 2-butynyl, 2-methyl-2-propynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl and 5-hexynyl.
As used herein the term xe2x80x9cdivalent (C2-C6)alkynylene radicalxe2x80x9d means a hydrocarbon chain having from 2 to 6 carbon atoms, at least one triple bond, and two unsatisfied valencies.
As used herein the term xe2x80x9ccycloalkylxe2x80x9d means a saturated alicyclic moiety having from 3-8 carbon atoms and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.
As used herein the term xe2x80x9ccycloalkenylxe2x80x9d means an unsaturated alicyclic moiety having from 3-8 carbon atoms and includes, for example, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl and cyclooctenyl. In the case of cycloalkenyl rings of from 5-8 carbon atoms, the ring may contain more than one double bond.
As used herein the term xe2x80x9carylxe2x80x9d refers to a mono-, bi- or tri-cyclic carbocyclic aromatic group, and to groups consisting of two covalently linked monocyclic carbocyclic aromatic groups. Illustrative of such groups are phenyl, biphenyl and napthyl.
As used herein the term xe2x80x9cheteroarylxe2x80x9d refers to a 5- or 6- membered aromatic ring containing one or more heteroatoms, and optionally fused to a benzyl or pyridyl ring; and to groups consisting of two covalently linked 5- or 6- membered aromatic rings each containing one or more heteroatoms; and to groups consisting of a monocyclic carbocyclic aromatic group covalently linked to a 5- or 6- membered aromatic rings containing one or more heteroatoms;. Illustrative of such groups are thienyl, furyl, pyrrolyl, imidazolyl, benzimidazolyl, thiazolyl, pyrazolyl, isoxazolyl, isothiazolyl, triazolyl, thiadiazolyl, oxadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, 4-([1,2,3]-thiadiazoly-4-yl)phenyl and 5-isoxazol-3-ylthienyl.
As used herein the unqualified term xe2x80x9cheterocyclylxe2x80x9d or xe2x80x9cheterocyclicxe2x80x9d includes xe2x80x9cheteroarylxe2x80x9d as defined above, and in particular means a 5-7 membered aromatic or non-armoatic heterocyclic ring containing one or more heteroatoms selected from S, N and O, and optionally fused to a benzene ring, including for example, pyrrolyl, furyl, thienyl, piperidinyl, imidazolyl, oxazolyl, thiazolyl, thiadiazolyl, pyrazolyl, pyridinyl, pyrrolidinyl, pyrimidinyl, morpholinyl, piperazinyl, indolyl, benzimidazolyl, maleimido, succinimido, phthalimido and 1,3-dioxo-1,3-dihydro-isoindol-2-yl groups.
The term xe2x80x9cesterxe2x80x9d or xe2x80x9cesterified carboxyl groupxe2x80x9d means a group R9O(Cxe2x95x90O)xe2x80x94 in which R9 is the group characterising the ester, notionally derived from the alcohol R9OH.
The term xe2x80x9cthioesterxe2x80x9d means a group R9S(Cxe2x95x90O)xe2x80x94 or R9S(Cxe2x95x90S)xe2x80x94 or R9O(Cxe2x95x90S)xe2x80x94 in which R9 is the group characterising the thioester, notionally derived from the alcohol R9OH or the thioalcohol R9SH.
Unless otherwise specified in the context in which it occurs, the term xe2x80x9csubstitutedxe2x80x9d as applied to any moiety herein means substituted with up to four substituents, each of which independently may be (C1-C6)alkyl, (C1-C6)alkoxy, phenoxy, hydroxy, mercapto, (C1-C6)alkylthio, amino, halo (including fluoro, chloro, bromo and iodo), trifluoromethyl, nitro, xe2x80x94COOH, xe2x80x94CONH2. xe2x80x94COORA, xe2x80x94NHCORA, xe2x80x94CONHRA, xe2x80x94NHRA, xe2x80x94NRARB, or xe2x80x94CONRARB wherein RA and RB are independently a (C1-C6)alkyl group.
As used herein the terms xe2x80x9cside chain of a natural alpha-amino acidxe2x80x9d and xe2x80x9cside chain of a non-natural alpha-amino acidxe2x80x9d mean the group Rx in respectively a natural and non-natural amino acid of formula NH2xe2x80x94CH(Rx)xe2x80x94COOH.
Examples of side chains of natural alpha amino acids include those of alanine, arginine, asparagine, aspartic acid, cysteine, cystine, glutamic acid, histidine, 5-hydroxylysine, 4-hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, xcex1-aminoadipic acid, xcex1-amino-n-butyric acid, 3,4-dihydroxyphenylalanine, homoserine, xcex1-methylserine, ornithine, pipecolic acid, and thyroxine.
In natural alpha-amino acid side chains which contain functional substituents, for example amino, carboxyl, hydroxy, mercapto, guanidyl, imidazolyl, or indolyl groups as in arginine, lysine, glutamic acid, aspartic acid, tryptophan, histidine, serine, threonine, tyrosine, and cysteine, such functional substituents may optionally be protected.
Likewise, the side chains of non-natural alpha amino acids which contain functional substituents, for example amino, carboxyl, hydroxy, mercapto, guanidyl, imidazolyl, or indolyl groups, such functional substituents may optionally be protected.
The term xe2x80x9cprotectedxe2x80x9d when used in relation to a functional substituent in a side chain of a natural or non-natural alpha-amino acid means a derivative of such a substituent which is substantially non-functional. For example, carboxyl groups may be esterified (for example as a C1-C6 alkyl ester), amino groups may be converted to amides (for example as a NHCOC1-C6 alkyl amide) or carbamates (for example as an NHC(xe2x95x90O)OC1-C6 alkyl or NHC(xe2x95x90O)OCH2Ph carbamate), hydroxyl groups may be converted to ethers (for example an OC1-C6 alkyl or a O(C1-C6 alkyl)phenyl ether) or esters (for example a OC(xe2x95x90O)C1-C6 alkyl ester) and thiol groups may be converted to thioethers (for example a tert-butyl or benzyl thioether) or thioesters (for example a SC(xe2x95x90O)C1-C6 alkyl thioester).
There are several actual or potential chiral centres in the compounds according to the invention because of the presence of asymmetric carbon atoms. The presence of several asymmetric carbon atoms gives rise to a number of diastereomers with R or S stereochemistry at each chiral centre. The invention includes all such diastereomers and mixtures thereof. Presently it is preferred that the stereochemical configuration at the carbon atom carrying the R2 group is R, and the configuration of the carbon atom carrying the R3 group is S.
In the compounds for use according to the invention and in the novel compounds of the invention:
R1 may be, for example, hydrogen, methyl, or trifuoromethyl. Hydrogen is currently preferred.
R2 may be, for example:
C1-C6 alkyl, C3-C6 alkenyl or C3-C6 alkynyl;
phenyl(C1-C6 alkylxe2x80x94, phenyl(C3-C6 alkenyl)xe2x80x94 or phenyl(C3-C6 alkynyl)-optionally substituted in the phenyl ring;
cycloalkyl(C1-C6 alkyl)-, cycloalkyl(C3-C6 alkenyl)- or cycloalkyl(C3-C6 alkynyl)-optionally substituted in the phenyl ring;
heterocyclyl(C1-C6 alkyl)-, heterocyclyl(C3-C6 alkenyl)- or heterocyclyl(C3-C6 alkynyl)- optionally substituted in the heterocyclyl ring;
4-phenylphenyl(C1-C6 alkyl)-, 4-phenylphenyl(C3-C6 alkenyl)-, 4-phenylphenyl(C3-C6 alkynyl)-, 4-heteroarylphenyl(C3-C6 alkyl)-, 4-heteroarylphenyl(C3-C6 alkenyl)-, 4-heteroarylphenyl(C3-C6 alkynyl)-, optionally substituted in the terminal phenyl or heteroaryl ring;
Specific examples of such groups include methyl, ethyl, n- and iso-propyl, n- and iso-butyl, n-pentyl, iso-pentyl 3-methyl-but-1-yl, n-hexyl, n-heptyl, n-acetyl, n-octyl, methylsulfanylethyl, ethylsulfanylmethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-ethoxymethyl, 3-hydroxypropyl, allyl, 3-phenylprop-3-en-1-yl, prop-2-yn-1-yl, 3-phenylprop-2-yn-1-yl, 3-(2-chlorophenyl)prop-2-yn-1-yl, but-2-yn-1-yl, cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylpropyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylpropyl, furan-2-ylmethyl, furan-3-methyl, tetrahydrofuran-2-ylmethyl, tetrahydrofuran-2-ylmethyl, piperidinylmethyl, phenylpropyl, 4-chlorophenylpropyl, 4-methylphenylpropyl, 4-methoxyphenylpropyl, benzyl, 4-chlorobenzyl, 4-methylbenzyl, and 4-methoxybenzyl.
Presently preferred groups at R2 are n-propyl, n-butyl, n-pentyl, benzyl and cyclopentylmethyl
R may be, for example, hydrogen or methyl, with hydrogen being presently preferred.
R3 may be, for example
C1-C6 alkyl, phenyl, 2,-3-, or 4-hydroxyphenyl, 2,-3-, or 4-methoxyphenyl, 2,-3-, or 4-pyridylmethyl, 2,-3-, or 4-hydroxybenzyl, 2,-3-, or 4-benzyloxybenzyl, 2,-3-, or 4-C1-C6, alkoxybenzyl, or benzyloxy(C1-C6alkyl)- group; or
the characterising group of a natural xcex1 amino acid, for example benzyl, iso-propyl, isobutyl, methyl or 4-methoxyphenylmethyl, in which any functional group may be protected, any amino group may be acylated and any carboxyl group present may be amidated; or
a group xe2x80x94[Alk]nR7 where Alk is a (C1-C6)alkyl or (C2-C6)alkenyl group optionally interrupted by one or more xe2x80x94Oxe2x80x94, or xe2x80x94Sxe2x80x94 atoms or xe2x80x94N(R12)xe2x80x94 groups [where R12 is a hydrogen atom or a (C1-C6)alkyl group], n is 0 or 1, and R7 is an optionally substituted cycloalkyl or cycloalkenyl group; or
a benzyl group substituted in the phenyl ring by a group of formula xe2x80x94OCH2COR8 where R8 is hydroxyl, amino, (C1-C6)alkoxy, phenyl(C1-C6)alkoxy, (C1-C6)alkylamino, di((C1-C6)alkyl)amino, phenyl(C1-C6)alkylamino, the residue of an amino acid or acid halide, ester or amide derivative thereof, said residue being linked via an amide bond, said amino acid being selected from glycine, xcex1 or xcex2 alanine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, serine, threonine, cysteine, methionine, asparagine, glutamine, lysine, histidine, arginine, glutamic acid, and aspartic acid; or
a heterocyclic(C1-C6)alkyl group, either being unsubstituted or mono- or di-substituted in the heterocyclic ring with halo, nitro, carboxy, (C1-C6)alkoxy, cyano, (C1-C6)alkanoyl, trifluoromethyl (C1-C6)alkyl, hydroxy, formyl, amino, (C1-C6)alkylamino, di-(C1-C6)alkylamino, mercapto, (C1-C6)alkylthio, hydroxy(C1-C6)alkyl, mercapto(C1-C6)alkyl or (C1-C6)alkylphenylmethyl; or
a group xe2x80x94CRaRbRc in which:
each of Ra, Rb and Rc is independently hydrogen, (C1-C6)alkyl, (C2-C6)alkenyl, (C2-C6)alkynyl, phenyl(C1-C6)alkyl, (C3-C8)cycloalkyl; or
Rc hydrogen and Ra and Rb are independently phenyl or heteroaryl such as pyridyl; or
Rc is hydrogen, (C1-C6)alkyl, (C2-C6)alkenyl, (C2-C6)alkynyl, phenyl(C1-C6)alkyl, or (C3-C8)cycloalkyl, and Ra and Rb together with the carbon atom to which they are attached form a 3 to 8 membered cycloalkyl or a 5- to 6-membered heterocyclic ring; or
Ra, Rb and Rc together with the carbon atom to which they are attached form a tricyclic ring (for example adamantyl); or
Ra and Rb are each independently (C1-C6)alkyl, (C2-C6)alkenyl, (C2-C6)alkynyl, phenyl(C1-C6)alkyl, or a group as defined for Rc below other than hydrogen, or Ra and Rb together with the carbon atom to which they are attached form a cycloalkyl or heterocyclic ring, and Rc is hydrogen, xe2x80x94OH, xe2x80x94SH, halogen, xe2x80x94CN, xe2x80x94CO2H, (C1-C4)perfluoroalkyl, xe2x80x94CH2OH, xe2x80x94CO2(C1-C6)alkyl, xe2x80x94O(C1-C6)alkyl, xe2x80x94O(C2-C6)alkenyl, xe2x80x94S(C1-C6)alkyl, xe2x80x94SO(C1-C6)alkyl, xe2x80x94SO2(C1-C6) alkyl, xe2x80x94S(C2-C6)alkenyl, xe2x80x94SO(C2-C6)alkenyl, xe2x80x94SO2(C2-C6)alkenyl or a group xe2x80x94Qxe2x80x94W wherein Q represents a bond or xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94SOxe2x80x94 or xe2x80x94SO2xe2x80x94 and W represents a phenyl, phenylalkyl, (C3-C8)cycloalkyl, (C3-C8)cycloalkylalkyl, (C4-C8)cycloalkenyl, (C4-C8)cycloalkenylalkyl, heteroaryl or heteroarylalkyl group, which group W may optionally be substituted by one or more substituents independently selected from, hydroxyl, halogen, xe2x80x94CN, xe2x80x94CO2H, xe2x80x94CO2(C1-C6)alkyl, xe2x80x94CONH2, xe2x80x94CONH(C1-C6)alkyl, xe2x80x94CONH(C1-C6alkyl)2, xe2x80x94CHO, xe2x80x94CH2OH, (C1-C4)perfluoroalkyl, xe2x80x94O(C1-C6)alkyl, xe2x80x94S(C1-C6)alkyl, xe2x80x94SO(C1-C6)alkyl, xe2x80x94SO2(C1-C6)alkyl, xe2x80x94NO2, xe2x80x94NH2, xe2x80x94NH(C1-C6)alkyl, xe2x80x94N((C1-C6)alkyl)2, xe2x80x94NHCO(C1-C6)alkyl, (C1-C6)alkyl, (C2-C6)alkenyl, (C2-C6)alkynyl, (C3-C8)cycloalkyl, (C4-C8)cycloalkenyl, phenyl or benzyl.
Examples of particular R3 groups include benzyl, phenyl, cyclohexylmethyl, pyridin-3-ylmethyl, tert-butoxymethyl, n-propyl, iso-propyl, iso-butyl, sec-butyl, tert-butyl, 1-benzylthio-1-methylethyl, 1-methylthio-1-methylethyl, and 1-mercapto-1-methylethyl. Presently preferred R3 groups include methyl benzyl, tert-butyl, iso-butyl, phenyl and isopropyl.
Examples of particular ester and thioester groups R4 groups include those of formula xe2x80x94(Cxe2x95x90O)OR9, xe2x80x94(Cxe2x95x90O)SR9, xe2x80x94(Cxe2x95x90S)SR9, and xe2x80x94(Cxe2x95x90S)OR9 wherein R9 is (C1-C6)alkyl, (C2-C6)alkenyl, cycloalkyl, cycloalkyl(C1-C6)alkyl-, phenyl, heterocyclyl, phenyl(C1-C6)alkyl-, heterocyclyl(C1-C6)alkyl-, (C1-C6)alkoxy(C1-C6)alkyl-, (C1-C6)alkoxy(C1-C6)alkoxy(C1-C6)alkyl-, any of which may be substituted on a ring or non-ring carbon atom or on a ring heteroatom, if present. Examples of such R9 groups include methyl, ethyl, n-and iso-propyl, n-, sec- and tert-butyl, 1-ethyl-prop-1-yl, 1-methyl-prop-1-yl, 1-methyl-but-1-yl, cyclopentyl, cyclohexyl, allyl, phenyl, benzyl, 2-, 3- and 4-pyridylmethyl, N-methylpiperidin-4-yl, 1-methylcyclopent-1-yl, adamantyl, tetrahydrofuran-3-yl and methoxyethyl.
Presently preferred are compounds of formula (IB) wherein R4 is a carboxylate ester of formula xe2x80x94(Cxe2x95x90O)OR9, wherein R9 is benzyl, cyclopentyl, isopropyl or tert-butyl.
Specific examples of compounds useful as antibacterial agents in accordance with the invention include those of the preparative examples herein, and pharmaceutically or veterinarily acceptable salts thereof.
Compounds of formula (I) may be prepared by causing an acid of formula (II) or an activated derivative thereof to react with an amine of formula (III) 
wherein R1, R2, R3 and R4 are as defined in general formula (I) except that any substituents in R1, R2, R3 and R4 which are potentially reactive in the coupling reaction may themselves be protected from such reaction, and R25 is as defined in relation to formula (I) above, and optionally removing protecting groups from R1, R2, R3 and R4.
Compounds of formula (II) may be prepared by N-formylation, for example using acetic anhydride and formic acid, of compounds of formula (IV) 
wherein R1, R2 and R25 are as defined in relation to formula (I) and R26 is a hydroxy protecting group, and thereafter removing the protecting group R26.
A compound of general formula (IV) may be prepared by reduction of an oxime of general formula (V) 
wherein R1, R2, R25 and R26 are as defined above. Reducing agents include metal hydrides (eg sodium cyanoborohydride in acetic acid, triethylsilane or boranelpyridine) and hydrogenation.
A compound of general formula (V) can be prepared by reaction of a xcex2-keto carbonyl compound of general formula (VI) 
wherein R1, R2, and R26 are as defined above, with an O-protected hydroxylamine. xcex2-keto carbonyl compounds (VI) may be prepared by acylation of the enolate derived from a carbonyl compound of formula (VII) or (VIIA) 
wherein R2 and R26 are as defined above, and Xc is a chiral auxiliary, with a compound of formula (VII) 
wherein R1 is as defined above and Z is a leaving group such as chloro or alkoxy. Chiral enolates of type (VIIA) have been described by Evans (J. Am. Chem. Soc., 104, 1737, (1982)).
Another method for the preparation of a compound of general formula (IV) is by Michael addition of a hydroxylamine derivative to an xcex1, xcex2-unsaturated carbonyl compounds of general formula (IX) 
wherein R1, R2, and R26 are as defined above. The xcex1,xcex2-unsaturated carbonyl compounds (IX) may be prepared by standard methods.
Further details of the synthetic routes to compounds for use in accordance with the invention appear in the preparative examples herein.
Salts of the compounds for use in accordance with the invention include physiologically acceptable acid addition salts for example hydrochlorides, hydrobromides, sulphates, methane sulphonates, p-toluenesulphonates, phosphates, acetates, citrates, succinates, lactates, tartrates, fumarates and maleates. Salts may also be formed with bases, for example sodium, potassium, magnesium, and calcium salts.
Compositions with which the invention is concerned may be prepared for administration by any route consistent with the pharmacokinetic properties of the active ingredient(s).
Orally administrable compositions may be in the form of tablets, capsules, powders, granules, lozenges, liquid or gel preparations, such as oral, topical, or sterile parenteral solutions or suspensions. Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinyl-pyrrolidone; fillers for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricant, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants for example potato starch, or acceptable wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, glucose syrup, gelatin hydrogenated edible fats; emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters such as glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents.
For topical application to the skin, the active ingredient(s) may be made up into a cream, lotion or ointment. Cream or ointment formulations which may be used for the drug are conventional formulations well known in the art, for example as described in standard textbooks of pharmaceutics such as the British Pharmacopoeia.
The active ingredient(s) may also be administered parenterally in a sterile medium. Depending on the vehicle and concentration used, the drug can either be suspended or dissolved in the vehicle. Advantageously, adjuvants such as a local anaesthetic, preservative and buffering agents can be dissolved in the vehicle.
In the hospital setting to combat severe bacterial infections, the active ingredient may be administered by intravenous infusion.
Safe and effective dosages for different classes of patient and for different disease states will be determined by clinical trial as is required in the art. It will be understood that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, rate of excretion, drug combination and the severity of the particular disease undergoing therapy.
Although it may be of interest to establish the mechanism of action of the compounds used in the present invention, it is their ability to inhibit bacterial growth per se which is of practical significance. Without wishing to be bound by any specific mode of action or mechanism by which the compounds operate, it is presently believed that the antibacterial activity of the compounds with which the invention is concerned may be due, at least in part, to inhibition of bacterial polypeptide deformylase (PDF) enzyme.
Bacterial polypeptide deformylase (PDF)(for example EC 3.5.1.31) is a family of metalloenzymes which is essential for bacterial viability, its function being to remove the formyl group from the N-terminal methionine residue of ribosome-synthesised proteins in eubacteria. Mazel et al. (EMBO J. 13(4):914-923, 1994) have recently cloned and characterised a PDF. As PDF is is essential to the growth of bacteria and there is no eukaryotic counterpart to PDF, Mazel et al. (ibid), Rajagopalan et al. (J. Am. Chem. Soc. 119:12418-12419, 1997) and Becker et al., (J. Biol Chem. 273(19):11413-11416, 1998) have each proposed that PDF is an excellent anti-bacterial target.
The following preparative examples describe the synthesis of compounds having antibacterial activity, in accordance with the invention.
1H and 13C NMR spectra were recorded using a Bruker DPX 250 spectrometer at 250.1 and 62.9 MHz, respectively. Mass spectra were obtained using a Perkin Elmer Sciex API 165 spectrometer using both positive and negative ionisation modes. Infra-red spectra were recorded on a Perkin Elmer PE 1600 FTIR spectrometer.
Analytical HPLC was performed on a Beckman System Gold, using Waters Nova Pak C18 column (150 mm, 3.9 mm) with 20 to 90% solvent B gradient (1 ml/min) as the mobile phase. [Solvent A: 0.05% TFA in 10% water 90% methanol; Solvent B: 0.05% TFA in 10% methanol 90%/], detection wavelength at 230 nm. Preparative HPLC was performed on a Gilson autoprep instrument using a C18 Waters delta prep-pak cartridge (15 xcexcm, 300 A, 25 mm, 10 mm) with 20 to 90% solvent B gradient (6 ml/min) as the mobile phase. [Solvent A water; Solvent B: methanol], UV detection was at 230 nm.
The following abbreviations have been used in the examples:
DMFxe2x80x94N,N-Dimethylformamide
HOBTxe2x80x941-Hydroxybenzotriazole
EDCxe2x80x94N-(3-Dimethylaminopropyl)Nxe2x80x2-ethylcarbodiimide hydrochloride
HClxe2x80x94Hydrochloric acid
THFxe2x80x94Tetrahydrofuran